Stretching of artificial yarn



Feb. 12, 1946. T. G. FiNZEL 2,394,540

STRETCHING OF ARTIFICIAL YARN Filed Aug. 20, 1943 it f T he to n. G.Finz E1 INVENTOR.

BY 4WA ATTORNEY Patented Feb. 12, 1946 UNITED STATES PATENT OFFICESTRETCHING or ARTIFICIAL YARN Theron G. Finzel, Kenmore, N. Y., assignorto E. I. du Pont de Nemours & Company, Wilmington, Del., a corporationof Delaware Application August 20, 1943, Serial No. 499,327

3 Claims. (Cl. 8-132) This invention relates to a method for increas-More particularly, the invention relates to a method for heat-treatingand stretching untwisted yarn of. synthetic, thermoplastic,filamentforming material whereby to increase the tenacity of the, yarn.

This application is a continuation-in-part of my copending applicationSerial No. 366,769 filed November 22, 1940. K

It is known to stretch artificial thermoplastic yarn and particularlycellulose derivative yarn which has been softened by heat. All of theknown processes, however, suffer from the defect that filaments makingup the yarn invariably adhere to one another, thereby impartingharshness to the yarn and rendering the same inferior in quality.

This invention has as an object a method for plasticizing yarn ofsynthetic, thermoplastic, filament-forming material and stretching thesame without causing the filaments to adhere to each other. A furtherobject is the provision of a method for heat treating thermoplasticcellulose derivative yarn, such as cellulose acetate yarn, to plasticizethe same and stretching the yarn while in the plastic state to produce ayarn free of stuck or adhering filaments. These and other objects willmore clearly appear hereinafter.

I have found that if an untwisted yarn or synihetic, thermoplastic,filament-forming material. such as cellulose acetate or acrylonitrilepolymer, is first spread to a ribbon whereby to separate and to alignall of the filaments in substantially the same plane. and the ribbon issoftened through contact with a heated roll and then stretched in thesoftened condition. a yarn of greatly enhanced tenacity is producedwhich yarn is at the same time soft to the touch and is of all aroundsuperior quality. By first spreading the yarn to a ribbon. substantiallyall filaments thereof are brought into direct contact with the surfaceof the heated roll. The yarn may be stretched to any des red degree, saytwo, five. ten or even more times its original length. Cellulose acetatespun in the conventional manner possesses a tenacity of about 1.4 toabout 1.7 grams per denier. Improvement in tenacity to 2.5 or more gramsper denier is achieved by the herein described method.

Untwisted yarn of any synthetic, thermoplastic, filament-formingmaterial may be treated in accordance with the principles of thisinvention. As representative of these thermoplastic filawent-formingmaterials may be mentioned cellulose esters such as cellulose acetate,cellulose propionate, cellulose butyrate, and cellulose nitrate;cellulose mixed esterssuch as cellulose acetate propionate, andcellulose acetate butyrate; cellulose ethers such as. ethyl celluloseand benzyl cellulose; mixed cellulose ethers, e. g. ethyl laurylcellulose; mixed cellulose ether-esters such as ethyl cellulose acetateand methyl cellulose propionate; and noncellulosic thermoplasticmaterials such as acrylonitrile polymers, nylon, vinyl esters. vinylethers, methacrylates, polystyrene, and Vinyon.

Referring to the accompanying drawing wherein the method and apparatussuitable for carry-' ing out the method of this invention areillustrated diagrammatically, Fig. 1 is a diagrammatic representation ofan arrangement of means suitable for carrying out the invention; Figs. 2and 3 show one method for varying the time contact of the yarn with thehot roll; Fig. 4 is a crosssection on the line A--A of Fig. 3; Fig. 5shows auxiliary means for heating the yarn on the heated roll; Fig. 6 isa plan view of a preferred means for spreading the yarn; and Fig. '7 isa section on the line BB of Fig. 6.

In Fig. 1, a thermoplastic yarn such a cellulose acetate yarn possessingno twist and of any reasonable denier and comprised of a plurality offilaments is unwound from a supply package (not shown) and passed arounda feed or snubbing roller I and thread advancing roller 2 used to feedthe untwisted cellulose acetate yarn over a guide and then through ayarn spreading device 3 onto a heated cylinder roll 4. Rolls l and 4rotate at the same peripheral speed. The yarn is softened on the hotsurface of roll 4 and is withdrawn from roll 4 over a guide roller 5 ata speed greater than the peripheral speed of roll 4. The ratio of yarndraw-off speed to the peripheral speed of roll 4 may be two, five. tenor more. Rolls l and 4 are driven in a counterclockwise direction, asindicated. After the yarn is cooled below the softening temperature, itmay be twisted in any well-known manner. After st etching, the tenacityof the yarn is materiallv increased and the yarn denier is reduced inpro-. portion to the stretch ratio.

The yarn must remain in-contact with roll 4 for such a length of time toeffect sufiicient softening so as to allow stretching of the celluloseacetate yarn at a tension of from 0.01 to 0.5 gram per denier of thestretched yarn. The time of contact may be controlled by the diameter ofthe heating roll, the speed of the roll. or the angle of contact alpha(or) (Figs. 2 and 3) of the yarn on the roll. Obviously, the higher theperipheral speed of the roll, the greater must be the angle or contactalpha. I

The cylinder 4 is heated in any suitable manner, as for instance, byelectrical means, high pressure steam, or vapor or liquids, tosumciently high temperature to efl'ect a suitable softening of the yarnin contact therewith.

Fig. 4 shows a section through A-A of Fig. 3.

This illustrates one method of heating roll 4.

' Shaft G of roll 4 is supported by a bearing I around which bearing aninsulating layer 8, such as mica, etc., is wound. On top of theinsulating layer 8 and close to the inner surface of roll 4, there iswound-a 'helical coil 9 of alloy wire having a high electricalresistance to act as an electrical heating ducing the necessary time ofheating and improving the uniformity of heatingas compared with theheating characteristics of the simple hot roll.

In Figs. 6 and '7, details of a preferred form of spreading device areshown. The device consists of two resilient thin sheets such as springsteel or spring brass leaves or other sheets which are suitablysupported and allowed to exert a mild pressure against each other. Asyarn passes between these flat surfaces, suilicient pressure is broughtto bear on the untwisted yarn to flatten the yarn into a form of aribbon wherein the filaments lie in substantially a single plane. Ifyarn of a heavy denier is used, a number of the above describedspreading devices may be used in series to an advantage. Another methodfor spreading and separating the filaments of a yarn into ribbon-likeform may consist of a series of rods over the sur faces of which theuntwisted yarn is passed. Other methods for spreading the filaments of ayarn may consist of a device which directs air jets against the yarn andthen allows the separated filaments to pass over a flat surface. The useof an electrical charge applied to the yarn which causes the filament toballoon out and then passing the separated filaments over a flat surfacemay be applied to advantage.

Application of the method of this invention is further illustrated bythe following examples.

Example I A 3000 denier cellulose acetate yarn (about 54% combinedacetic acid) containing 150 filaments and possessing no twist was fedonto a heated roll set-up, the diagrammatic sketch of which is shown inFig. 2. The yarn was fed onto the heated roll at the rate of 242" perminute and drawn from the roll at the rate of 1280" per minute. Thediameter of the heated roll was 2" and its temperature was approximately240 C. The filament spreading device consisted of two spring steelleaves 0.0045" thick, pressing mildly against each other. The averagetension of the yarn as it was drawn from the heated roll wasapproximately 65 grams. After cooling, the stretched yarn was twisted tothe extent of two turns per inch. Upon testing at 70 F. and 60% relativehumidity, it showed a tenacity of 2.5 grams per denier.

Example II A 3000 denier, 150 filament cellulose acetate aseasso' yarn(about 54% combined acetic acid) possessing no twist was fed through afilament spreading device onto a heated roll, as illustrated in Fig, 2,at

the rate 0! 128" per minute and was withdrawn .1

from the heated roll at the rate of 1280" per minute with an averageyarn tension of 60 grams. The roll was heated to a temperature of 256 C.and the angle of contact of the yarn with the roll was approximately150. The stretched yam showed a tenacity of 2.2 grams per denier.

Example III A 580 denier, 58 filament cellulose acetate yarn (about 54%combined acetic acid) possessing no twist was passed through a spreadingdevice and 256" per minute and was drawn from the heated roll at therate of 1280" per minute under an average tension of approximately 10grams. The angle of contact of the-yam with the roll was approximately203 and the temperature of the heated roll was approximately 240 C. Thetemperature of the air between the heated roll and the auxiliary heatingelement 1 I as shown in Fig. 5 was approximately 215 C. After twistingthe cold yarn to the extent of approximately two turns .per inch, theyarn showed a tenacity of 2.3 grams Der denier.

Example IV A 440 denier, 40 filament, no twist yarn pre-' pared by dryspinning a solution-of acrylonitrile polymer of 103,000 averagemolecular weight (as determined by viscosity data using the Staudingerequation) dissolved in dimethyl formamide, was passed through a springleaf filament spreading device and around a hot roll as shown in Fig. 2.The yarn was fed onto a heated roll at the rate of inches per minute anddrawn from this roll at the rate of 1450 inches per minute, therebystretching the yarn .ten times. The diameter of the hot roll was 1%" andthe angle of contact ofthe yarn with the hot roll was approximately 330while the temperature to which the roll-was heated was -180 C.

The unstretched yam of 440 denier showed a tenacity of 0.6 gram perdenier. The yarn was stretched down to 42-45 denier and showed atenacity of 4.3 grams per denier.

The copending application of George Henry Latham, Serial No. 562,012,filed November 4, 1944 (a continuation-in-part of his copendingapplication ,Serial No. 447,466, filed June 17, 1942) describes thedissolving of acrylonitrile polymers in dimethyl formamide and in othersolvents and the formation of shaped articles from such solutions. Thecopending application of Daniel C. Meloon, Serial No. 496,397, filedJuly 28., 1943, describes the heat-stretching of acrylonitrile polymerarticles. No claim is made in the present application to the inventionsof said Latham and Meloon copending applications and the invention ofthis application is limited as set forth in the claims.

It is understood that my invention is not limitedto the precise detailsdescribed, but is susceptible rather to-wide variation and comprehendsall modifications and equivalents falling within the spirit of theinvention as defined by the claims.

I claim:

1. The process which comprises spreading an untwisted yam comprised of aplurality of filaments of synthetic, thermoplastic, filamentformingmaterial to the point where all of the 15 filaments are separated andlie in substantially 3. The process which comprises flattening anuntwisted yarn comprised of filaments of acrylonitrile polymer to thepoint where all of the filaments are separated and lie in substantiallythe same lane, passing the flattened yarn over a heated rotating rollwhereby to render the yarn plastic, and stretching the plastic yarnwhile it is in the separated state.

. THERON G. FINZEL.

